Unfortunately, this is a known wish request(FORMS-9678) and there is no Webhook event for Forms at this moment. But if you can provide more business scenario that would help a lot for our engineering team to prioritize this wish.

About the 3LO, yes, Forms support 3LO only, if you want pure automation without user interact, please hold on, we are working on a new feature which could support you to use 3LO without user interaction, but it's still not ready yet at this moment(2025/3/13), if you are urgent to try that, please contact us directly for more details.